Condensed Matter Seminar - Collin Broholm, The Johns Hopkins University - "Continuum Excitations in Crystalline Magnets"

Mon, Mar 4, 2013, 1:15 pm to 2:30 pm
PCTS Seminar Room
I present inelastic neutron scattering data from one- two- and three-dimensional insulating magnetic materials at low temperatures that do not display a coherent resonant mode of excitation. Instead, momentum resolved spectra take the form of bounded continua. I interpret the spectra as evidence for fractionalization of a spin flip into distinct quasi-particles. The unifying feature of the quantum magnets examined is a ground state that does not break rotational or translational symmetries – conventional Neel order having been disfavored by competing interactions and/or low dimensionality. I discuss the nature of the quasi-particles based on the neutron scattering data, the underlying lattice structure, and the spin Hamiltonian. The talk features inelastic neutron scattering data from novel instrumentation at the NIST Center for Neutron Research and the ORNL Spallation Neutron Source, which is dramatically improving our ability to probe atomic scale dynamics in condensed matter.